Car bombs and a rocket barrage struck a predominantly Shiite neighbourhood in Baghdad, flattening homes and killing at least 62 people, officials said on Monday.
The rockets were apparently fired from a mostly Sunni district targeted by US troops in a crackdown against the sectarian violence roiling the capital.
About 140 were injured in the Sunday night attack on the Zafraniyah neighbourhood in southern Baghdad, which began about 7:15 pm with two car bombs and a barrage of an estimated nine rockets, Defence Ministry spokesman Col Saddoun Abu al-Ula said.
He said the rockets appeared to have been fired from the neighbourhood of Dora, which has been the focus of thousands of US troops sent to try to restore peace in Baghdad.
"This is terrorism against the whole nation," said Ali al-Sayedi, a municipal council member.
Mohammad al-Kaabi, a photographer, said the initial rocket attack drew scores of people rushing to rescue the injured when a parked car exploded.
"We were transferring the injured when about an hour later a rocket hit a three-floor building, destroying it," he told the agency.
Reporters could not reach the scene on Sunday night because of a curfew but on Monday they saw scenes of indiscriminate destruction.
Massive slabs of concrete, which once were ceilings of a multistory apartment, lay atop each other in a collapsed heap.
A pedestrian bridge was ripped off its mooring at one end and had fallen at an angle, crushing a car underneath.
One rocket had punched a hole in the roof of a house, and store fronts were blasted inward.
The blackened and crumpled wreckage of an overturned car lay nearby. Several cars were twisted out of shape, their seats stained with dry blood.
On the front passenger seat of one car, pink wrapping paper of what was probably a gift fluttered in the breeze amid the blanket of grey and brown dust covering the destruction around it.
A middle-aged man in a bloodstained disdasha, the traditional Arab robe, walked aimlessly, hitting his face with his hands in grief.
Residents said his six children were crushed to death when his house collapsed.
The head of a municipal council, Mohammed al-Rubaie, told Iraqi government television on Monday that the death toll was 62.
He gave no precise number of injured but officials late Sunday put the figure at more than 140.
Several large explosions were heard in central Baghdad at sunrise Monday, but it was unclear where they came from.
The attack in Zafraniyah was the deadliest since the United States announced last month that it was reinforcing troop strength in the capital following a surge in sectarian violence that the United Nations estimated killed nearly 6,000 Iraqis in May and June.
The complex style of the assault was similar to a July 27 attack of mortars, rockets and car bombs on another mostly Shiite district, Karradah, which killed 31 people. Police said the missiles that struck Karradah also were fired from Dora.
A Sunni extremist group, the al-Sahaba Soldiers, claimed responsibility for the Karradah attack to punish Shiites for supporting the "crusaders," or Americans, and the "treacherous" Iraqi government, which is dominated by Shiites.
Muhanna Yassin, who lives in Zafraniyah, said the attack left "a total mess" with "bodies of the dead and injured scattered around in the streets _ old, young, women and children."
"The ground shook underneath us and there was chaos everywhere," he said in a telephone interview.
He said many of the victims were cut by flying glass and debris, leaving parts of the streets soaked in blood.
The multiple attacks were part of the grisly pattern of Sunni-Shiite violence that American officials consider the greatest threat to Iraq's stability more than three years after the US-led invasion toppled Saddam Hussein's regime.
US commanders are sending nearly 12,000 US and Iraqi soldiers into the capital to curb the surge of sectarian violence, which was described by the US ambassador to Iraq, Zalmay Khalilzad, on Sunday as "the principal problem here."
"I believe that the sectarian violence is serious," he said on CNN.
On Sunday, US and Iraqi soldiers began searching more than 4,000 homes in the Sunni neighbourhood of Amariyah while conducting a similar operation simultaneously in the Shiite district of Shula, the US command said.
"The operations are designed to reduce the level of murders, kidnappings, assassinations, terrorism and sectarian violence in northwest Baghdad and to reinforce the Iraqi government's control," a statement by the US command said.
Sectarian tensions have been rising following the February 22 bombing at a Shiite shrine in Samarra, which triggered a wave of reprisal attacks against Sunni mosques and clerics.
Tens of thousands of Iraqis have fled their homes since then, seeking refuge in areas where their Muslim sect is in the majority.
Much of the violence has been blamed on sectarian militias and armed groups that target members of the rival community. Prime Minister Nouri al-Maliki, a Shiite, has promised to disband the militias, some of which are linked to figures in his own government.